A WERNER-TYPE ALKYL COBALT(III) COMPOUND - FORMATION OF A CARBON COBALT BOND DEMONSTRATED BY C-13, CO-59 NMR AND X-RAY STRUCTURE DETERMINATIONS

The coordinated alkyl cation (1,6-diamino-3-thia-4-hexanido)(1,4,7-triazacyclononane)cobalt(III), [Co(tacn)(C-aeaps)]2+ has been prepared in aqueous solution by base addition to (3-thia-1,6-hexanediamine)(1,4,7-triazacyclononane)cobalt(III), [Co(tacn)(aeaps)]3+. The unusual alkyl cobalt(III) coordination compound has been characterized by UV-VIS and NMR spectroscopy as well as X-ray crystallography. The ligand field band in the visible region is of the usual low intensity, and so the carbanion is an innocent ligand. Its DELTA(Oh) value seems not very different from that of an amine ligand. The coupling constants between the Co-59 and C-13 nuclei were determined for [Co(tacn)(C-aeaps)]2+ and a few others to make comparisons possible. Single bonds are found to have J(C-Co) values of 80-90 Hz. The starting material can be considered a Bronsted acid with the conjugate base being a carbanion complex. The starting material and its conjugate base were isolated as perchlorates, and they have been characterized by X-ray diffraction methods at 110 K. Both form orthorhombic crystals with space group Pbca. Crystal data for [Co(tacn)(aeaps)](ClO4)3: M = 620.74 g mol-1, a = 28.094(4), b = 10.580(3), c = 14.620(1) angstrom, V = 4345(2) angstrom3, F(000) = 2560, Z = 8, D(m) = 1.882, D(calc) = 1.898 g cm-3, MoK-alpha = 0.710 73 angstrom, mu = 13.21 cm-1, R = 0.042 for 3590 unique reflections. Crystal data for [Co(tacq)(C-aeaps)](ClO4)2: M(r) = 521.29, a = 18.169(5), b = 15.824(4), c = 13.888(4) angstrom, V = 3993(3) angstrom3, F(000) = 2168, Z = 8, D(calc) = 1.734 g cm-3, mu = 12.76 cm-1, R = 0.074 for 1400 unique reflections. The latter compound displays disorder of both the cation and one of the perchlorate ions. The disorder of the [Co(tacn)(C-aeaps)]2+ ion corresponds to the presence of the two different configurations of the carbon-bound ligand at the cobalt site.